This application is based on application No. JP 2000-72245 filed in Japan, the contents of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an improved truss actuator drive control device in which two displacement units are connected at their respective ends and the driven member is driven by the above ends.
2. Description of the Related Art
One example of a known conventional truss actuator comprises a thin plate-shaped truss actuator comprising a piece of sheet steel cut out such that two displacement units cross each other at a right angle, and piezoelectric elements are applied to both sides of each displacement unit.
In order to drive a driven member using this actuator, a method is used in which the piezoelectric elements on the side of each displacement unit are caused to resonate such that the top of each crossing displacement unit is induced to diagonally collide with the driven member and move the driven member in a prescribed direction.
However, in the conventional drive method described above, because the tops of the sheet steel piece collide with the driven member in a linear fashion, the problems of significant noise and vibration arise as well as the problem that the sheet steel and driven member suffer substantial wear. In addition, because the method lacks a mechanism by which to detect the amount of displacement of the piezoelectric elements, the problem arises that it becomes difficult to control the speed of the driven member. Furthermore, because the conventional method lacks a mechanism by which to detect the displacement of the displacement units caused by the resonance driving, the displacement of the displacement units deviates from a prescribed value due to the fluctuation in the load on the actuator or in the environment in which the actuator is used, for example, and the output level to the driven member cannot be controlled at a constant level.
The present invention was created in view of these problems, and an object thereof is to provide an improved truss actuator. In other words, an object of the present invention is to reduce noise, vibration and wear in a truss actuator. Another object of the present invention is to provide a truss actuator drive control device in which the speed of the driven member may be controlled. Furthermore, yet another object of the present invention is to provide a truss actuator drive control device that can control the output to the driven member at a constant level regardless of fluctuations in the load on the actuator or in the use environment.
In order to attain these and other objects, the truss actuator drive control device according to one aspect of the present invention is a drive control device for a single-side drive-type truss actuator that comprises a base frame, two displacement units each fixed to the base frame on the distal end such that the distal ends cross each other, a drive unit comprising a synthesizing unit located at the distal ends of the displacement units, and a pressure unit that causes the synthesizing unit to come into pressure contact with the driven member, which is the object of driving, wherein one of the two displacement unit is caused to oscillate and this oscillation is transmitted to the other driven displacement unit in order to drive the driven member, and wherein said drive control device includes two displacement detecting units that respectively detect the displacements of the two displacement units, a phase difference detecting unit that detects the phase difference between the detected displacement values of the displacement detecting units, a target phase difference setting unit that sets the target phase difference, a deviation determining unit that determines the deviation between the phase difference from the phase difference detecting unit and the target phase difference from the target phase difference setting unit, and a frequency changing unit that changes the drive frequency of the displacement unit based on the result of the determination by the deviation determining unit.
In the above aspect, one of the two displacement units is driven to oscillate, and this oscillation is transmitted to the other driven displacement unit, such that the driven member is driven. When this occurs, the phase difference between the displacements detected by each displacement detecting unit located on each displacement unit of the actuator is detected by the phase difference detecting unit. The deviation of the phase difference detected by the phase difference detecting unit and the target phase difference from the target phase difference setting unit, i.e., the imbalance of the detected phase difference relative to the target phase difference, is determined by the deviation determining unit, and based on the result of this determination, the frequency changing unit changes the oscillation frequency such that the above deviation is eliminated, and therefore, the detected phase difference and the target phase difference ultimately match each other, so that the output to the driven member may be controlled at a constant level regardless of fluctuations in the load on the actuator or in the use environment.
In the truss actuator drive control device according to another aspect of the present invention, a memory stores the target phase difference to be set in the target phase difference setting unit, and the target phase difference can be inputted by operator.
In the above aspect, because the target phase difference set by the target phase difference setting unit is changed depending on the target phase difference data stored in the memory, control may be performed such that the speed of the driven member may be changed to a desired speed.
The truss actuator drive control device according to another aspect of the present invention is a single-side drive-type truss actuator that comprises a base frame, two displacement units each fixed to the base frame on the distal end such that the distal ends cross each other, a drive unit comprising a synthesizing unit located at the distal ends of the displacement units, and a pressure unit that causes the synthesizing unit to come into pressure contact with the driven member, which is the object of driving, wherein one of the two displacement units is driven to oscillate and this oscillation is transmitted to the other driven displacement unit using a 90xc2x0 target phase difference in order to drive the driven member, and wherein said drive control device includes two displacement detecting units that respectively detect the displacement of the two displacement units as a pulse signal, a phase difference detecting unit that detects the phase difference between the pulse signals output from the displacement detecting units, a first signal generating unit that generates a signal the level of which changes depending on the phase difference and based on the detection signal output from the phase difference detecting unit and a second signal generating unit that generates a signal the level of which changes in the opposite direction depending the phase difference and based on the detection signal output from the phase difference detecting unit, a deviation determining unit that determines the deviation between the two signals based on the two signals output from the first and second signal generating units, and a frequency changing unit that changes the drive frequency of the displacement unit based on the result of the determination by the deviation determining unit.
In the above aspect, because the levels of the signals output from the first and second signal generating units change in opposite directions, the median value of the signals becomes the target phase difference when the driven displacement unit is to be driven using a 90xc2x0 target phase difference relative to the driving displacement unit. Consequently, the frequency may be changed by seeking the deviation of the detected phase difference from the target phase difference and based on the result thereof, such that the target phase difference setting unit may be eliminated.
Here, where the phase difference between the driving displacement unit and the driven displacement unit is xc2x190xc2x0, the locus of the synthesizing unit becomes a circular locus, and in other cases (except for where the phase difference is 0xc2x0, when the locus becomes a linear locus), the locus of the synthesizing unit becomes an oval locus. Because the phase difference has the relationship with the drive frequency that is shown in FIG. 2 and described below, the synthesizing unit moves in a circular or oval fashion, noise and oscillation are reduced, and the wear of the synthesizing unit and driven member may be reduced.
In a specific construction representing the above aspect, the phase difference detecting unit may comprise a logic circuit that outputs a pulse signal having a duty ratio corresponding to the phase difference between the pulse signals output from the two displacement detecting units, the first signal generating unit may comprise a first smoothing circuit that smoothes the pulse signal output from the logic circuit, the second signal generating unit may comprise an inverter circuit that inverts the phase of the pulse signal output from the logical circuit and a second smoothing circuit that smoothes the pulse signal output from the inverter circuit, and the deviation determining unit may comprise a comparison circuit that compares the levels of the two signals respectively output from the first and second signal generating units.
In the truss actuator drive control device according to yet another aspect of the present invention, the two displacement units may each comprise a layered piezoelectric element, and the displacement detecting units may each comprise a detection circuit that detects the displacement of each piezoelectric element based on the value of the electric current that flows in the piezoelectric element.
The above aspect uses the relationship in which the displacement of the piezoelectric element is essentially proportional to the value of the electric current flowing therein, and therefore, detection of the values of the electric currents flowing in the piezoelectric element by the displacement detecting units enables speed control of the driven member.
In the truss actuator drive control device according to yet another aspect of the present invention, each of the displacement detecting units may be mounted on each of two displacement units and comprise a distortion gauge that detects the displacement thereof.
In the above aspect, because the displacement of each displacement unit is detected by a distortion gauge, inaccurate phase detection caused by the pulsation of the electric current value in the driving displacement unit that occurs when the value of the electric currant flowing in the layered piezoelectric element is detected when rectangular waves are directly used for the drive signal may be prevented.